[Todos] Seminario INQUIMAE/ DQIAyQF Lunes 15 de septiembre 13 hs

[andrea en qi.fcen.uba.ar]

Lunes 15 de septiembre, 13 hs.

Lugar: INQUIMAE, Departamento de Química Inorganica, Analitica y Qui­mica
Física, Facultad de Ciencias Exactas y Naturales. Universidad de Buenos
Aires. Ciudad Universitaria. Pabellón 2.

Aula de Seminarios del 3er piso

Resumen de la charla:
Spectroscopic studies on molecular mechanism of energy conversion
by cytochrome bc1 complex.

Artur Osyczka

Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics
and Biotechnology, Jagiellonian University, Kraków, Poland


Cytochrome bc1 complex is a key enzyme of the biological energy conversion
systems in the majority of organisms, from photosynthetic bacteria to
human mitochondria. Structurally it is a homodimer consisting of two
cytochrome b subunits, two cytochromes c1 and two Rieske proteins. It is
embedded in the bioenergetic membranes where it contributes to the
generation of a protonmotive force by a series of quinone
oxidation/reduction reactions. Side reactions often involve generation of
reactive oxygen species (ROS). Our group uses spectroscopic tools in
combination with molecular biology to investigate both catalytic and side
reactions to develop understanding how the enzyme works at molecular
level.
Benefiting from magnetic properties of the metal redox cofactors we
developed EPR-based techniques to monitor changes in the distances between
them that are part of the catalytic cycle [1]. Together with the genetic
knocking out of the individual cofactors, this allowed us to identify
mechanism and reaction sequence primarily responsible for ROS generation
[2,3]. We also detected by EPR two populations of semiquinone that can be
assigned as intermediate state of the catalytic reactions performed by the
enzyme [4].
One of the intriguing questions concerns the possibility of electronic
communication between the monomers, implicated from structure. To address
this issue we engineered a fusion protein system that allowed us to break
the symmetry of a homodimer by introducing specific mutation/mutations
only in one monomer. This way we created a series of mutants designed to
test all of the possible paths of electron transfer within the complex,
including the inter-monomer electron exchange, in light-induced
spectroscopic kinetic measurements [5, 6]. This was complemented by
specific variants of the fusion proteins that allowed testing in vivo the
functionality of inter-monomer electron connection [7].
Our findings offer new perspective on mechanism of efficient energy
conversion, suppression of ROS, and regulatory function of cytochrome bc1.

1. Sarewicz M et al. (2009) Biochemistry 48
2. Borek A et al. (2008) Biochemistry 47
3. Sarewicz M et al. (2010) Biochim Biophys Acta 1797
4. Sarewicz M et al. (2013) Biochemistry
5. Å’wierczek M et al. (2010) Science 329
6. Czapla M et al. (2013) Biochim Biophys Acta 1827
7. Ekiert R et al. (2014) Biochim Biophys Res Comm 451


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